Field of the Invention
The present invention relates to the field of combustion engines, and more particularly to combustion engines equipped with double supercharging.
Description of the Prior Art
The supercharging of an engine increases the quantity of air and fuel mixture within the cylinders of the engine in comparison with normal operation. Supercharging, and especially double supercharging, make it possible to increase the efficiency of a combustion engine without changing the rotational speed. This is because engine torque (and therefore power) is dependent on the angle formed between the connecting rod and the crankshaft, on the pressure of the gases inside the cylinder, referred to as the Mean Effective Pressure (or MEP) and on the pressure of the amount of fuel introduced. For example, for a gasoline engine, if the amount of gasoline introduced into the cylinder is increased, then the mass of air (oxidizer) must also be increased proportionately in order to ensure complete combustion of this fuel (the same air/fuel ratio is maintained).
In order to obtain this supercharging, the mass of gas on the intake side is increased, making it possible to increase the quantity of fuel. In order to do that, the gaseous mixture on the intake side of the engine (essentially comprising air and optionally burnt gases) is compressed. This compression may be performed by the compressor of a turbocharger driven by the exhaust gases by means of a turbine, or compression may be performed by a separate mechanical compressor which may be driven by the engine crankshaft. Double supercharging is referred to when the gaseous mixture on the intake side is compressed twice: for example a first time by a compressor of the turbocharger and a second time by a mechanical compressor situated in the engine intake circuit. Conventionally, the mechanical compressor, which is dynamically controlled, compensates for the start-up inertia of the turbocharger.
In order to control the pressure of the air on the intake side, referred to as the boost pressure, it is possible to alter the way in which the two compressors behave. On the one hand, in order to control the air passing through the mechanical compressor, a valve is controlled, which is referred to as a bypass valve, which is positioned in parallel with the compressor and diverts air toward the compressor according to its openness, and which is controlled. Furthermore, when the compressor is driven by the engine crankshaft and is controlled by a clutch is inserted between a reduction gear and the mechanical compressor. The clutch allows the mechanical compressor to be activated or deactivated. Conventionally, the mechanical compressor is deactivated for high engine speeds (the limiting speed is dependent on the drive ratio between the crankshaft and the mechanical compressor). On the other hand, in order to control the compression of air by the turbocharger, the turbocharger is equipped with a variable geometry turbine (VGT), which when controlled changes the rotational speed of the turbocharger and therefore a change in the compression.
Thus equipped, the combustion engine and the supercharging system needs instrumentation to determine various pressures and temperatures within the supercharging circuit. The measured values are used for controlling the supercharging, the engine, and diagnosing of the operation of the supercharging.
FIG. 1 depicts a prior art combustion engine equipped with double supercharging and instrumentation. An engine (1) is equipped with an intake circuit and with an exhaust circuit. Arranged in the intake circuit in the direction in which the air flows are: an air filter (7), the compressor of the turbocharger (2), a first charge air cooler (6), a mechanical compressor (3) and a second charge air cooler (5). Arranged in parallel with the mechanical compressor is a diverting or bypass circuit comprising a bypass valve (4). In the exhaust circuit is a variable geometry turbine (VGT) identified as (2). The mechanical compressor (3) is driven by the crankshaft of the engine (1) via a transmission, which is a belt, and by a clutch (11). The charge air coolers (5 and 6) allow the air which becomes heated during the successive compressions to be cooled.
Furthermore, as depicted, the engine may comprise an exhaust gas recirculation (EGR) circuit (8) comprising a cooler (10) and a valve (9) which is referred to as an EGR valve. The circulating burnt gaseous mixture with the fresh air between the air filter (7) and the compressor of the turbocharger (2). The engine (1) as depicted comprises four cylinders. These last two characteristics (the EGR and the number of cylinders) are independent of the invention and are nonlimiting.
According to this prior art, the engine (1) is equipped with four sensors making it possible respectively to measure a pressure Pavcm of a gaseous mixture upstream of a mechanical compressor (3), a temperature Tavcm upstream of the mechanical compressor (3), and a boost pressure Psural and boost temperature Tsural on the intake side of the engine (1). The use of four sensors is a restriction of the design of the engine notably in terms of bulk, mounting, location of the sensors, etc., and is expensive.